At age 7, the number of ADHD symptoms rose 13 percent for each unit of increase in the ratio of omega-6 to omega-3.

The researchers said a balance between the two fatty acids is important, because they have opposing functions. Omega-6 promotes inflammation; omega-3 is an anti-inflammatory.

Omega-6 is found in certain vegetable and plant oils, seeds and nuts, while omega-3 is generally found in fish and fish oil, according to the Mayo Clinic.

While the ratio was associated with the number of ADHD symptoms, this was only at age 7 and it was not linked to an ADHD diagnosis, according to the study. Also, only an association and not a cause-and-effect link was seen.

"Our findings are in line with previous studies that established a relationship between the omega-6/omega-3 ratio in mothers and various early neurodevelopmental outcomes," said lead author Monica Lopez-Vicente. She's a researcher at the Barcelona Institute for Global Health (ISGlobal).

"Although the association was not clinically significant, our findings are important at the level of the population as a whole," Lopez-Vicente noted in an institute news release.

Study co-author Jordi Julvez, also from ISGlobal, said the study adds to a growing body of research about the importance of maternal diet during pregnancy.

"The nutrient supply during the earliest stages of life is essential in that it programs the structure and function of the organs, and this programming, in turn, has an impact on health at every stage of life," Julvez said.

"As the brain takes a long time to develop, it is particularly vulnerable to misprogramming. Alterations of this sort could therefore lead to neurodevelopmental disorders," he explained.